1. Field of the invention
The present invention relates to a process for opening polyamide reverse osmosis membranes to increase the salt passage thereof for certain specialized purposes such as forming very high concentrates of various liquid or liquifiable food products.
2. Prior Art
U.S. Pat. No. 4,643,902 discloses using ultrafiltration to remove bacteria from juices while passing flavor and aroma components of the juice. The bacteria are then treated to inactivate them and the permeate recombined with the retentate which contained the bacteria.
U.S. Pat. No. 3,617,550 discloses a process for concentrating a feed solution by forcing the feed solution through a series of high rejection membranes, recycling or discarding the permeate and then further concentrating the retentate using a series of low rejection membranes where the osmotic pressure of the retentate exceeds the working pressure of the low rejection membranes. Preferably the permeate from the low rejection membranes is recycled. The process enables the production of concentrates having an osmotic pressure of several thousand psi which is above the working pressure of reverse osmosis membranes.
U.S. Pat. No. 3,836,457 discloses a system for concentrating by recycling the permeate from reverse osmosis membranes.